Okay, I got a call from a customer I've known for a few years. His second floor has some issues. Fixed the first couple no problem. The third was the reason I'm writing. (okay, keyboarding) No power to one circuit. Power at the breaker, but disappears between the panel and the first device. Traced the cable back to an exterior wall. While I'm figuring out how to re-run another circuit the HO asks me to take a look at some taped up wires in the ceiling of the master bedroom. I undo one of them and it's a splice for the second floor wiring. Shouldn't these splices have remained accessible? If not for the HO, I would've been there all day. Pics are at ElectricalPhotos.com

The HO said it was a prefab. I don't know if that meant the whole second floor came as one or several pieces. He wants to get rid of those connections and put them in a splice box. He'll paint the cover to match the ceiling and get the cover as flush as possible. Thanks for the info.

Those AMP connectors are UL Listed to be installed without a box; but they still need to be accessible.

That is not really true

They come under 545.13

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545.13 Component Interconnections. Fittings and connectorsthat are intended to be concealed at the time of on-siteassembly, where tested, identified, and listed to applicablestandards, shall be permitted for on-site interconnection ofmodules or other building components. Such fittings and connectorsshall be equal to the wiring method employed in insulation,temperature rise, and fault-current withstand and shallbe capable of enduring the vibration and minor relative motionsoccurring in the components of manufactured buildings

The installation instructions say

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B. Building Site and Dwelling SiteThe separate modules of a building ordwelling assembled on location are tobe connected electrically by thesimple plug-in connection (including a mechanical latch)of mating pairs thereby providing circuit continuity.The connected pairs may or may not be fastened inplace. The connected pairs may or may not beconcealed by the installation

When my double-wide was set up they told me that these were used to connect the 2 units together electrically. There was a removable drywall panel in a closet that allowed access to clip them together after the units were in place.

I was told that the panel couldn't be permanently patched in afterwards because the connecteors had to stay accessible in case they needed to be repaired or replaced.

Concealing them was okay just as long as they could be gotten to at a later date.

The instructions and the code are pretty clear unless you have a local restriction.For a while Amp was even marketing these for retrofits in regular 1&2 family dwellings but that was stopped in 99 or so.

They were seen as a way to fix that old "burned up TW wire in the ceiling luminaire" problem. They said you could splice on a piece of NM-b and shove it up in the ceiling then install an old work ceiling box. They used 334.40(B) to justify it.

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(B) Devices of Insulating Material. Switch, outlet, and tap devices of insulating material shall be permitted to be used without boxes in exposed cable wiring and for rewiring in existing buildings where the cable is concealed and fished. Openings in such devices shall form a close fit around the outer covering of the cable, and the device shall fully enclose the part of the cable from which any part of the covering has been removed. Where connections to conductors are by binding-screw terminals, there shall be available as many terminals as conductors.

Someone looked into it and decided these particular devices were only approved in manufactured homes, leaving open the question, what does 334.40(B) really apply to?